As was originally planned, Voyager 2 would make its closest approaches to Callisto, Ganymede, Europa, and Amalthea before encounter with Jupiter. Because of the difference in the trajectories of the two spacecraft, Voyager 2 would see the faces of Callisto and Ganymede not seen by Voyager 1. The most important difference, however, was that the second Voyager would fly much closer to Europa than Voyager 1 did, giving scientists their first good look at the mysterious streaks scratched on the surface of that bright golden world. Voyager 2 would also have a closer flyby of Ganymede, giving us a second chance to examine its strange “snowmobile tracks.” The major loss, of course, was Io, which would be seen from Voyager 2 only at distances of a million kilometers or more. [Illustration: Io appeared in front of Jupiter as seen by Voyager on June 25, at a range of 12 million kilometers. At a resolution of about 200 kilometers, the bright and dark spots on the satellite are just beginning to be resolved, but it was not possible to determine if any eruptions were still in progress. [P-21719C]] The Encounter Wednesday, July 4. (_Range to Jupiter, 5.3 million kilometers; range to Earth, 921 million kilometers_). While most of the nation celebrated Independence Day with picnics, sports events, and fireworks, the scientists and engineers at JPL were working around the clock. Voyager 2 had already entered Jupiter’s territory, crossing the bow shock for the first time on July 2 at a distance of 99 R_J from Jupiter, indicating that the magnetosphere had expanded in the interval between the two encounters. At about noon on July 3, the spacecraft encountered the magnetopause, but on July 4, the data from the particles and fields instruments were ambiguous. Apparently the magnetosphere was pulsating in response to changing pressures, and the spacecraft was playing tag with the rapidly shifting boundaries of the bow shock and the magnetopause. As the low energy charged particle instrument began to measure particles coming from inside the Jovian magnetosphere, it became apparent that some important changes had taken place since Voyager 1’s encounter. From the composition of the particles, it appeared that they were largely of solar origin, unlike the heavy concentrations of ions of sulfur and oxygen seen by Voyager 1. Scientists began to speculate that the Io volcanoes, which presumably eject sulfur and oxygen into the magnetosphere, might have declined in activity. In the evening, the first images of Io at a resolution high enough to allow the volcanic plumes to be seen would be beamed back to Earth. ENCOUNTER DISTANCES FOR VOYAGER 2 Object Range to Center at Closest Best Image Resolution Approach (kilometers) (km per line pair)